unit: test-sae: zero out frame buffers

Not all the authenticate frame elements are set and were assumed
to be zero. Since alloca does not memset data it needs to be
done explicitly.

unit/test-sae.c

@@ -202,6 +202,7 @@ static size_t setup_auth_frame(struct authenticate_frame *frame,
 				uint16_t trans, uint16_t status,
 				const uint8_t *data, size_t len)
 {
+	memset(frame, 0, sizeof(struct authenticate_frame));
 	memcpy(frame->hdr.address_2, addr, 6);
 
 	frame->hdr.fc.type = MPDU_TYPE_MANAGEMENT;